1. Field of the Invention
This invention relates generally to a planetary gear unit and more specifically to a planetary gear unit for an automatic transmission of a motor vehicle, the transmission including a passage introducing lubricating oil into a portion of the transmission wherein a plurality of planet pinions are rotatably disposed.
2. Description of the Prior Art
In general, it is well known that each of a plurality of planet pinions disposed in a planetary gear unit is rotatably mounted on a respective pinion shaft supported on an arm member, whereby the planet pinions revolve around a sun gear of the planetary gear unit.
Therefore, in a conventional planetary gear unit, passage means are used for introducing lubricating oil into the inner surface of each planet pinion and which comprises a first conduit for drawing lubricating oil from a surrounding portion of a sun gear is provided in a plate attached to the arm member and a second conduit for introducing the lubricating oil from the first conduit into the inner surface of each planet pinion. Alternatively, a first conduit formed by drilling the arm member for drawing lubricating oil from a surrounding portion of a sun gear is communicated with the second conduit for introducing lubricating oil from the first conduit into the inner surface of each planet pinion.
In these types of gear units, however, the conduit for drawing lubricating oil in the former example is formed with the additional plate which thus requires an additional member to be used in the gear unit. This can cause an increase in the number of parts required and scaling up of the gear unit. On the other hand, the first conduit for drawing lubricating oil in the latter example is formed by providing a conduit in the arm member. As a result, accurate formation of the first conduit communicated with the second conduit is difficult.